In the case of hydrostatic transmission vehicles, the speed control is usually effected by a speed control lever by means of which it is possible to order a variation of cylinder displacement and thus output of the pump or pumps supplying fluid under pressure to the hydraulic motors which effect the rotation of the driving running elements, the rotation speed of each of these driving running elements being proportional to the delivery supplying its hydraulic motor.
As regards the direction control, it is in general effected either by simple steering of the director running assembly in relation to the driving running assembly, as is the case for ordinary automobile vehicles, or by differentiation of the speeds of the driving running elements of the driving running assembly, as is the case for track-laying vehicles.
A control of direction by steering of a director running assembly necessitates minimum weight on the latter; it further requires the utilization of differentials between the right and left driving running elements of the driving running assembly:
On the other hand it is very flexible to utilize, as this utilization can be effected by a hand wheel the control of which advantageously responds to the natural reflexes of a driver.
A control of direction by differentiation of speeds between the right and left driving running elements of the driving running assembly is itself applicable only to vehicles of very short wheel-base, unless considerable ground scrubbing is accepted; moreover its utilization, usually effected by levers, lacks flexibility and does not respond to the natural reflexes of a driver; finally in general in this case there is not total independence between the speed and direction control systems.
However in French Pat. No. 1,573,169 of the April 8, 1968 there was described a rocker lever control system for direction and speed of automobile vehicles with hydrostatic transmission, permitting speed control by differentiation of speeds between the right and left driving running elements of the driving running assembly of such a vehicle, advantageously with utilization by hand wheel and total independence between the speed and direction control systems.
The rocker lever device as described in the said patent advantageously in turning permits directional piloting of the director running assembly coordinated coherently with the different speeds imposed moreover upon the right and left running elements of the driving running assembly, in order to obtain such turning.
Thus to a certain extent it permits a positive piloting of a transverse differential.
However in the above-mentioned patent the running elements of the director running assembly are not driving elements.
The present invention has in general for object a hydrostatic transmission vehicle which is controlled in direction by steering of a director running assembly and the director running assembly of which is likewise a driving assembly, this running assembly therefore being hereinafter called motor-director.
As is well-known, this arrangement advantageously permits increasing the traction power of such a vehicle and imparting higher mobility capacity to it.
More precisely, the hydrostatic transmission vehicle according to the invention is thus of the kind which bears on the ground by at least two longitudinally staggered running assemblies, namely a driving running assembly which can be controlled in speed by a speed control system, and a motor-director running assembly which can be reduced to one single running element and which on the one hand is mounted to pivot as a whole about a steering spindle under the control of a direction control system, and on the other hand can also be controlled in speed under the control of a speed control system. The vehicle drive is characterised in that a coupling connection is established between the speed control system of the motor-director running assembly and the speed control system of the driving running assembly. This coupling connection includes a rocker lever mounted for pivoting and having on each side of its pivot on the one hand a first arm, hereinafter called constant arm, by which it is linked to any one of the speed control systems and the projection of which upon a median rest position corresponding to straight-ahead travel of the vehicle is substantially constant, and a second arm, hereinafter called a variable arm, by which it is linked to the other of the speed control systems and the projection of which upon the median rest position is variable under the control of the direction control system.
In practice, the pivot of the rocker lever is carried by a slider mounted for movement in a first direction under the control of a cam, and its variable arm cooperates, through the intermediary of supplementary engagement means, with a drum piece which is linked to the corresponding speed control and is guided in displacement in a second direction perpendicular to the first, the said cam, which is mounted for rotation about an axis perpendicular to the two said directions at the point of intersection thereof, being keyed in rotation on the direction control system and having a cam profile in contact with which a lug fast with the said slider and coaxial with the pivot thereof is held applied.
According to a first form of embodiment the director profile of this cam is a circle passing through its axis of rotation.
As variant this director profile is a straight line segment obtained by geometric inversion of the above circular director profile in relation to the point of this circular director profile through which the axis of rotation of the said cam passes.
Whichever is the case, the coupling connection provided according to the invention permits application to the motor-director running assembly of a speed coordinated with that of the driving running assembly, either in a straight line or in turning.
In fact it ensures a determined variable ratio between on the one part the action exerted directly upon the speed control system of the driving running assembly from the speed control lever which in practice is available for this purpose to the driver of the vehicle, and on the other part the action which it transmits to the speed control system of the motor-director running assembly, this ratio depending upon the steering angle imparted moreover by the said driver to the motor-director running assembly with the aid of the direction control system which is likewise available to him for this purpose, and ensuring coherence of the speed of the motordirector running assembly with that of the driving running assembly.
This coupling connection thus to a certain extent permits of ensuring a positive piloting of a longitudinal differential.
It is advantageously next conjugated with that described in the above-mentioned French Patent, which permits a positive piloting of a transverse differential.
All the driving running elements of a hydrostatic transmission vehicle according to the invention are thus advantageously piloted in mutually coherent fashion, both in orientation and in speed.
In such a case, all the forces developed on the ground by such a vehicle advantageously combine for the direction of the vehicle, so that there is no tendency to side-slip or crab by such a vehicle, whatever is the distribution of the loads among its various running elements.